Small-angle neutron scattering of poly(gamma-benzyl L-glutamate) in deuterated benzyl alcohol

Small-angle neutron scattering has been used to study poly(gamma-benzyl L-glutamate) (PBLG) in deuterated benzyl alcohol (DBA) as the solution is brought from the isotropic phase into the gel phase. The results show that an aggregation of PBLG molecules exists up to 80 degrees C even in the isotropic phase and the size of the aggregate does not change with temperature within the isotropic phase for a given concentration. However, the size of the aggregate increases with concentration or as the gelation threshold is crossed. The measurement of fractal dimension at intermediate length scales of the aggregates in the isotropic phase shows that the aggregates are less dense at higher polymer concentrations. But at lower length scales of similar to 50 Angstrom, the mesh size of the aggregates in the isotropic phase decreases with increasing polymer concentration. Studies of the fractal dimension of the resultant gels show that the thermal history of the sample in the isotropic phase influences the gel microstructure. The fractal dimension of the PBLG-DBA gel obtained by a step quench procedure is higher than that of a gel obtained by a sudden quench. We have also observed that the local concentration gradients become sharper as the polymer concentration increases in the gel phase.